bit-tech.net

How the Xbox 360 affects PC gamers

Wowsa. So the Xbox 360 finally got announced. To be honest, I'm absolutely blown away. The specs are utterly mouthwatering, and the design and some of the thought that has clearly gone into making this a desirable bit of kit is simply outstanding.

Of course, whilst the console is important for its own sake, it also has profound implications for us PC enthusiasts, and that's what I'd like to talk a little about today.

So let's get the basics down. Xbox 360 uses 3 PowerPC cores on a single chip, each running at 3.2GHz. It sports the R500 graphics processor, which runs at 500MHz core, has a 10MB embedded DRAM architecture and a unified shader system. It sports 512MB of GDDR3 RAM, running at 700MHz, which is split between the main system and the graphics. 4 wireless controllers are supported, whilst the system sports a 20GB hard drive and a built-in Media Center Extender.

The processor, then. Let's get some context. PowerPC chips are made by IBM, and run the Apple PowerMac chips. Whilst we don't know the exact model numbers for these chips yet, they're clearly a variant on the G5 chip that runs the PowerMac, since the Xbox 360 development kits - what programmers use before final hardware is available - were Macs. Presently, the G5 operates at 2.7GHz, so for the 360 to be operating at 3.2GHz is a step up. The present dual-core Intel and AMD chips run at 3.2GHz and 2.4GHz respectively. IBM have squeezed three cores at 3.2GHz into this baby. Not only that, but each of those cores uses a form of HyperThreading (although it's not called HyperThreading) to process 2 threads each, meaning simultaneous execution of 6 threads.

"It's highly likely that we're going to be seeing more and more PC games come with built-in dual- or multi-core support"

Undoubtedly, the OS for this machine will be based, in some way, on Windows. Whilst Apple has long been known to have OSX code that works on x86 architecture, it now seems as if Microsoft has Windows code to work on PowerPCs chips.

What does the processor mean for PCs, then? Well, the first thing is that games for the 360 are going to be multi-threaded from day one, to take advantage of the massive threading performance that a 3-core CPU will have. Because of the unified development architecture that now encompasses the PC and the Xbox 360 - known as the XNA platform - it's highly likely that we're going to be seeing more and more PC games come with built-in dual- or multi-core support, since it will be relatively easy to convert over from the Xbox 360 version.

The architecture that sits beneath the processor is rather radical, and it's something that, quite honestly, we're still trying to get our heads around. Rather than using separate graphics and system memory, it appears that the Xbox 360 uses a unified memory architecture that splits the memory as it needs. The actual memory itself is GDDR3, the same stuff you'll find on the latest graphics boards from ATI. There's no physics processing unit, which is something that was rumoured a while back. Instead, Microsoft are banking on the triple-core to handle those kinds of calculations. We are rather unlikely to see this kind of shared memory architecture in PCs any time soon, because it would require a substantial redesign of the entire platform, which isn't something that either AMD or Intel are keen to do right now.

Back to top

Wil Harris


"48 pipelines is simply bonkers."

The graphics system uses the R500 GPU from ATI. Whilst all sorts of information has been flying round, here's what we know. R500 is an Xbox-only chip. R520, ATI's next PC part, is nothing like it. It won't be until R600 - possibly this time next year, or even early 2007 - that we see the Xbox-esque features on the PC. The GPU itself uses a unified shader architecture. That is, unlike PC graphics boards - which use a pixel shader pipeline and vertex shader pipeline - just one pipeline is used for both, which will, it is said, lead to more efficient programming and better performance. This is the one aspect of the Xbox 360 that has been debated already. Nvidia have gone on record as saying that they think a unified shader architecture is a bad idea, whilst ATI have gone on record as saying they think it's the way forward for PC graphics. Unfortunately for Nvidia, it's really Microsoft, with the DirectX specification (soon to be renamed Windows Graphics Foundation, when Longhorn finallly turns up) that writes the rules. Whilst WGF will support separate pixel and vertex pipelines, there can be little doubt that the coding will favour a unified architecture, and consequently, ATI.

Whilst ATI may have had to work incredibly hard, and divert a lot of resources to the Xbox 360 project to get everything to work properly, the payoff may well be a headstart over Nvidia when the next-generation PC graphics wars kick off.

Oh, and here's a number for you: 48 pipelines. The X850 uses 16, the R520 is mooted to have 32. 48 pipelines is simply bonkers.

The obvious query is how far a shared memory architecture will affect the performance. Well, ATI - the graphics providers for Xbox 3 - have integrated embedded DRAM onto the graphics processor, with 10MB of the stuff effectively acting as a cache for the graphics board. By having a large amount of extremely fast memory right next to the chip, it means that operations such as anti-aliasing can be done with almost no performance hit. Obviously, that's a big boon for large displays with comparatively low resolutions, such as TVs. The technology would clearly be of benefit in PCs, but again, the embedded DRAM technology won't be on the desktop until R600. By then, it may well be that Nvidia have adopted it too.

There are a couple of other things to note about the Xbox 360. The first is that it uses a liquid cooling system to keep the components cool. We suspect that it's heatpipe technology, similar to that used in servers, rather than a watercooling setup like we might build today. Hopefully, similar quiet, efficient solutions can be developed for the PC, because the solutions currently are less than optimal.

The gamepad the 360 uses is wireless, and charges its batteries over USB. The controller will also work with PCs, meaning an end to Xbox-to-USB converters, it seems.

The machine packs a 20GB hard drive, which isn't enough for a great deal of media storage. However, it does pack a Media Center Extender. This means that if you have a Media Center PC with all your music and videos on it, your Xbox 360 will be able to stream and play that media wirelessly. That's a fairly nifty feature.

All in all, then, the Xbox 360 is packing some technology that is going to make its way to the PC eventually, and that will influence the way that programmers work on the PC. It may well be a while before we see PC components that can keep pace with the new Xbox, and even when they do, we can bet they'll be a heck of a lot more expensive than the subsidised Xbox 360 will be.

With a European, Japanese and American launch scheduled for before Christmas, frankly, we can't wait to get our hands on one of these things.